1. Field of the Invention
The present invention relates to a coordinate input apparatus that optically detects a coordinate position that has been input on a coordinate input face with a pointer such as a finger in order to input or select information, a control method therefor and a program. In particular, the present invention relates to a detachable portable coordinate input apparatus, a control method therefor and a program.
2. Description of the Related Art
Conventionally, as a coordinate input apparatus as described above, coordinate input apparatuses (touch panel, digitizer and the like) employing various systems have been proposed or commercialized. For example, coordinate input apparatuses such as a touch panel, with which operation of an information processing apparatus such as a personal computer (PC) can be easily performed by touching a screen with a finger without using any special devices, are widely used.
There are various types of coordinate input systems for such coordinate input apparatuses, including a method using a resistance film, a method using ultrasonic waves, and the like. A method is known as a coordinate input method that uses light in which a retroreflecting member is provided on the outside of the coordinate input face, light from a light projecting unit is reflected by the retroreflecting member, and the light amount distribution of the reflected light is detected by a light receiving unit. In this method, a light path is blocked by pointing a position in the coordinate input region with a pointer such as a finger, and a pointed position is calculated by detecting the direction in which light is blocked (for example, see U.S. Pat. No. 4,507,557, Japanese Patent Laid-Open No. 2004-272353).
A configuration example obtained by generalizing the configuration disclosed in U.S. Pat. No. 4,507,557 is shown in FIG. 10. FIG. 10 shows sensor units 1L and 1R disposed on both sides of the coordinate input face, and a coordinate input effective region 3 that serves as a coordinate input face used to input coordinates. In addition, a retroreflecting member 4 that surrounds three sides of the coordinate input effective region 3 so as to reflect back incident light in the direction opposite to the incident direction is included.
The sensor units 1L and 1R each include a light projecting unit and a light receiving unit (not shown in the drawings). The light projecting unit irradiates the input face of the coordinate input effective region 3 with light that spreads substantially in parallel to the input face in a fan-like form. The light receiving unit receives returned light that has been reflected back by the retroreflecting member 4. The coordinate input apparatus can calculate the coordinate position input in the coordinate input effective region 3 based on the directions in which light is blocked (blocking angles θL and θR) detected by the two sensor units 1L and 1R and the distance between the sensor units 1L and 1R. Note that in FIG. 10, reference numeral 2 indicates a control circuit that controls the sensor units 1L and 1R, processes obtained signals output from the sensor units 1L and 1R, or outputs results of the processing to an external apparatus. Reference numeral 8 indicates a light-transmitting protection member for protecting the retroreflecting member 4.
Japanese Patent Laid-Open No. 2004-272353 discloses a specific configuration example of the light projecting unit and the light receiving unit in the sensor unit of the coordinate input apparatus employing an optical light-blocking system that is disclosed in U.S. Pat. No. 4,507,557.
In the configuration disclosed in Japanese Patent Laid-Open No. 2003-280802, a light guiding unit that is provided surrounding three sides of the coordinate input effective region and emits light to the side face that is substantially perpendicular to the light-guiding direction is shown instead of the retroreflecting member shown in U.S. Pat. No. 4,507,557 and Japanese Patent Laid-Open No. 2004-272353.
Furthermore, Japanese Patent Laid-Open No. 2001-43021 discloses a configuration to control turning on a light emitting unit for each sensor unit. Specifically, in order to prevent light emitted from the light emitting unit of one sensor unit from being received by the light receiving unit of the other sensor unit as disturbance light, control is performed such that light is emitted in alternation from the light emitting units of the sensor units.
Furthermore, Japanese Patent No. 4118664 discloses a configuration in which retroreflecting members are disposed at the top and bottom sides of the coordinate input effective region, and sensor units are disposed spaced apart from each other between the retroreflecting members and the coordinate input effective region.
However, with the conventional techniques described above, it is difficult to support a multiple display as shown in FIG. 11A, in other words, an increase in size or horizontal length of the coordinate input effective region due to the following reasons. Note that FIG. 11A assumes displaying of a single image in a single large screen by using three front projectors.
First, in the case where a plurality of coordinate input apparatuses are lined up to support multiple display, as in conventional techniques (see FIG. 11B), a retroreflecting member 4 is indispensable in a joint portion of coordinate input apparatuses. As a result, in addition to a problem of discontinuities in the displayed image, it is impossible to continuously perform coordinate pointing and operation through a region “a” to a region b in FIG. 11B, which greatly deteriorates operability. Specifically, in the multiple display, retroreflecting members 4 in joint portions are hindering elements.
In order to solve this problem, as shown in FIG. 11A, it is necessary to provide the retroreflecting member 4 on the outside of the display region of the multiple display. As clearly seen from FIG. 11A, a difference in the distance between a direction “a” and a direction b in FIG. 11A increases with an increase in the number of display faces. Accordingly, in the coordinate input apparatus of this type in which light projected by the light projecting unit reaches the retroreflecting member 4, and light that has been reflected back by the retroreflecting member 4 is detected by the light receiving unit, a difference in the amount of received light increases with this difference in distance (light path difference).
That is, even if the amount of light projected by the sensor unit 1L is constant regardless of the light projection direction, a relatively large amount of light is received in the direction “a”, and the smallest amount of light is received in the direction b due to the difference in distance. It is generally difficult to keep this difference within the dynamic range of a light receiving element (a photoelectric conversion element such as a CCD or a CMOS). Specifically, if settings are performed such that the amount of received light in the direction “a” corresponds to a maximum output value within the dynamic range, light in the direction b cannot be detected at all. Or, if light in an amount sufficient for detecting light in the direction b is projected, then the detection signal of light in the direction “a” saturates, which makes it difficult to obtain correct data.
In order to solve this problem, it is necessary to vary the amount of projected light according to the light projection direction by, for example, increasing the amount of light projected in direction b in FIG. 11A. In this manner, the amount of received light can be leveled, but at the same time, this inevitably causes a problem such as an increase in cost or size of the apparatus.
As a configuration for reducing the light path difference, as shown in FIG. 11C, a configuration is conceivable in which a larger number of sensor units 1L and 1R are disposed, and the display region is divided into the regions for detection by the respective sensor units. At this time, from the viewpoint of avoiding deterioration of operability described above, the retroreflecting members 4 are provided only at the top and bottom sides of the display region as shown in FIG. 11C, for example, such that no retroreflecting member 4 is present in the display region. Although the number of sensor units increases, the light path difference is reduced and thereby stable detection of optical signals becomes possible.
In the configuration disclosed in Japanese Patent No. 4118664, retroreflecting members are provided at opposite sides of the display region, and a light projecting unit and a light receiving unit are provided on the outside of the retroreflecting members. At this time, if projected light and received light have the same height from the coordinate input face (height in the normal line direction to the coordinate input face) as the retroreflecting members, the retroreflecting members block the light path. Thus, for the adopted configuration, projected light and received light have different heights from the coordinate input face (height in the normal line direction to the coordinate input face) from the height of the retroreflecting members. However, this causes a new problem as described below.
As shown in FIG. 12A, the configuration disclosed in Japanese Patent No. 4118664 includes sensor units 901 each including a light projecting unit and a light receiving unit between a retroreflecting member 903 and a coordinate input face 902. Light projected from the light projecting unit in a sensor unit 901 is reflected back by a retroreflecting member 903 provided at the side opposing that sensor unit 901, and received by the light receiving unit of the sensor unit 901. Accordingly, a hatched portion 908 corresponds to the light path. If a pointer 907 is disposed as shown in FIG. 12A, with respect to the sensor unit 901 on the left side, the light path (hatched portion 908) is not blocked. Thus the sensor unit 901 on the left side cannot detect the pointer 907. On the other hand, the light path (hatched portion 908) of the sensor unit 901 on the right side is blocked by the pointer 907, and thus the position information (direction) of the pointer 907 can be detected.
That is, in the state of the pointer 907, in which one of the sensor units can detect the position information (direction) and the other sensor unit cannot detect the position information (direction), it is impossible to calculate the pointed position of the pointer 907. It is when the pointer 907 approaches the coordinate input face 902 so that the pointer 907 sufficiently blocks the light path of the sensor unit 901 on the left side, in other words, it is when the pointer 907 has reached a position where the pointer 907 is about to touch the coordinate input face 902, that the pointed position can be detected. Accordingly, in the configuration disclosed in Japanese Patent No. 4118664, if the pointer 907 is separated from the coordinate input face 902, the position thereof cannot be detected stably. Hereinafter, the function that enables detection of the position of the pointer 907 even in a position separated from the coordinate input face is referred to as “proximity input”.
As a configuration that copes with this problem (problem that proximity input is impossible depending on the region), as shown in FIG. 12B, a configuration is conceivable in which a retroreflecting member is provided between the light projecting unit and the light receiving unit of the sensor unit 901. The retroreflecting member 903 is provided between a light projecting unit 910 and a light receiving unit 909 of the sensor unit 901 on the left side, and thereby the light path in which light from the light projecting unit 910 reaches a retroreflecting member 903 opposing thereto and the light path in which light from the retroreflecting member 903 opposing the light receiving unit 909 reaches the same are set as illustrated in FIG. 12B. In the case where the pointer 907 is in the same position as in FIG. 12A, although the pointer does not block the light path that reaches the light receiving unit 909 from the opposed retroreflecting member 903, it blocks the light path in which light from the light projecting unit 910 reaches the retroreflecting member 903 opposing thereto, and thus it is possible to detect the pointer 907. That is, this realizes a configuration in which detection is possible with the right and left sensor units 901, and proximity input is possible.
FIG. 12C illustrates the cross section of the sensor unit 901. In order to efficiently detect retroreflective light with this configuration, a distance L between the light projecting unit 910 and the light receiving unit 909 is set to be small. However, setting the distance L to be small is equivalent to setting a width h of the retroreflecting member 903 to be small. When the width h of the retroreflecting member is reduced, the retroreflective light is also reduced substantially in proportion to the width h.
Therefore, it is necessary to solve a contradiction that the distance L needs to be small in order to efficiently detect retroreflective light, although the distance L needs to be large in order to secure sufficient retroreflective light.